Cryogenic liquefying-refrigerating method and apparatus



, May 10, 1966 E. w. L. DAVIS ET AL 3,250,079

CRYOGENIC LIQUEFYING-REFRIGERATING METHOD AND APPARATUS Original Filed April 4, 1961 2 Sheets-Sheet 2 CHARCOAL 39\ TRAP INSULATED INVENTORS Elmer W.L. Davis BY Robert M. Lunn dwkm. 1 M

Attorney Patented May 10, 1966 3,250,079 CRYOGENIC LIQUEFYlNG-REFRIGERATING METHOD AND APPARATUS .Elmer W. L. Davies, Marblehead, and Robert M. Lunn,

Lexington, Mass., assignors to Arthur D. Little, Inc., Cambridge, Mass., a'corporation of Massachusetts Continuation of application Ser. No. 100,565, Apr. 4, 1961. This application Mar. 15, 1965, Ser. No. 439,841 12 Claims. (Cl. 62-9) gases including helium. There are of coursetechniques available for reducing the temperature of liquid helium to within a fraction of one degree Kelvin for particular purposes, but it is necessary first to provide a method and apparatus for liquefying the helium. It is also necessary to be able to liquefy other gases such as hydrogen neon, nitrogen and those having higher liquefaction temperatures.

Since in some cases it is necessary to work with liquid helium temperatures while in others it is necessary to use very cold gases for refrigeration it would be desirable to have a method and apparatus which could serve as a combination helium liquefier and refrigerator, The method and apparatus of this invention meet such a requirement.

US. Patent 2,458,894 discloses method and apparatus for liquefying helium and so-called cryostats constructed in accordance with that invention have found world-wide acceptance in providing reasonably large quantities of liquid helium. However, the present cryostat'is not designed to serve as 'a refrigerator or as a combination of a refrigerator and a helium liquefier. The apparatus and method of this invention represent improvements over US. Patent 2,458,894 in that it is possible to obtain great flexibility in operation in furnishing either liquefied helium, very low temperature refrigeration, or a combination of these.

It is therefore an object of this invention to provide apparatus which. may be employed in a dual capacity, that is to furnish very low-temperature refrigeration (as low as 4.2 K.) to an external load, or to furnish liquefied gases including helium. It is another object of this invention to provide apparatus of the character described which possesses built-in flexibility as to its performance both with respect to its ability to be rapidly switched from one operation to the other and to its ability to handle a a number of different gases. Another object is to provide apparatus which optimizes performance with size of equipment. Yet another object is to provide reliable apparatus capable of liquefying helium or of providing lowtemperature refrigeration down to 4.2 K. Yet another object is to provide apparatus of the character described which embodies a closed cycle refrigeration system requiring only minor amounts of make-up gas.

It is another important object of the present invention to provide a method of refrigerating and liquefying gases, the method being flexible enough to permit choosing either refrigerating or liquefying. It is another object to provide a reliable method for liquefying helium and other gases or for reducing the temperature of such gases and using the cold gases as a refrigerating fluid. These and other objects will become apparent in the following description of the invention.

The apparatus and method described in U.S.P. 2,458,- 894 achieves reliable and relatively rapid liquefaction of helium through the use of va plurality of expansion engines placed in series relationship, each one handling colder fluid than the one above. Each is, moreover, subjected to a colder atmosphere than its predecessor until the point is reached where final expansion through a Joule-Thomson valve can be employed to liquefy the helium. Precooling in that apparatus with liquid nitrogen is optional, its use resulting in essentially don-- blingthe output of liquid helium. In order to use the cryostat apparatus of U.S.P. 2,458,894 it is necessary to conduct experiments within a limited space Within the main heat exchanger or to remove the liquefied helium from the cryostat and transfer it to a Dewar or other suitable container. There are many instances however when it is necessary to have lowtemperature refrigeration as low as 4.2 K. which can be obtained through the use of cold helium which is actually not liquefied. In such instances it is also desirable to be able to supply a continuous flow of this cold gas to refrigerate an external load for an extended period of time. The helium cryostat of U.S.P. 2,458,894 is not capable of supplying this type of refrigeration to an external load, nor is it capable of flexible performance, that is of alternating between supplying refrigeration and supplying liquid helium. The apparatus and method of this invention are capable of this flexibility and operation and therefore as pointed out above represent a major improvement over the prior art.

The apparatus of this invention may be broadly defined as comprising, in addition to a source of compressed gas, first and second heat exchangers adapted to handle high-pressure gas and low-pressure gas in out-of-contact heat exchange, first and second expansion means, conduit means arranged to convey the compressed gas into the first heat exchanger, conduit means arranged to to convey cooled compressed gas from near the colder end of the first heat exchanger to the first expansion means and into the second heat exchanger and thence to the second expansion means, means for controlling the amountof flow of compressed gas to at least the second expansion means, conduit means for conveying cold low-pressure gas from the first expansion 'means to and from an external load (space to be cooled) including means for controlling the flow of gas to the external load and means for returning low-pressure gas to the. first heat exchanger, diffuser means for separating gas from liquid associated with the cold, low-pressure side of the second heat exchanger, and controlled-flow conduit mean-s for conveying low-pressure gas from the second heat exchanger to the first heat exchanger.

The low-temperature fluid refrigeration process of this invention comprises the steps of cooling compressed gas through out-of-contact heat exchange with low-pressure cold gas, simultaneously with said cooling condensing out impurities, expanding a first portion (which may be essentially all) of the cooled gas thereby to furnish a first supply of cold gas, returning the first supply of cold gas, either directly or by way of an external load, if refrigeration is to be accomplished, in a direction countercurrent.

to the flow of compressed gas thereby to accomplish the cooling step; and if liquefaction is desired further cooling at second portion of the cooled gas and expanding the second portion of further cooled gas to furnish a quantity of. liquefied gas and a second supply of cold gas, and returning the second supply of cold gas with the first supply to accomplish the cooling.

The apparatus and method of this invention may now be described in more detail with reference to the accompanying drawing in which FIG. 1 is a flow diagram showing the essential components of the apparatus of this invention; and

FIG. 2 is a modification of a portion of the apparatus of FIG. 1.

In FIG. 1 it will be seen that the portion of the apparatus which must be maintained at a temperature below normal room temperature is enclosed within a Dewartype vessel 10, which is made up of an outer wall 11 and an inner wall 12, these walls defining therebetween an annular space 14 which is evacuated by any suitable known method. Within the evacuated space 14 the lower portion of, inner wall 12 is surrounded by a radiation shield 16. It will be appreciated that the lower end of the dewar flask is the colder end, and that the radiation shield is required for minimizing heat transfer to inner wall 12. Precooling coils 18 are located around inner wall 12 and around radiation shield 16. Normally liquid nitrogen will be used and this is introduced through con duit 19 and removed through a conduit 20, both of these conduits entering and leaving evacuated space 14 through appropriate vacuum tight openings.

The following description will be presented in terms of an apparatus suitable for handling helium as the working fluid. It will be appreciated that-hydrogen, nitrogen, neon and the like may all be substituted for the helium. Obviously, any apparatus suitable for liquefying helium can be operated to handle the higher-boiling gases.

Before describing the working components located Within the dewar-type housing the auxiliary components which are more or less standard equipment and which are located outside the actual cryostat may be described. There is first a helium or other gas) supply 22, the makeup helium required from it being transferred by appropriate conduit 23 through a liquid nitrogen cooled trap 24 to be purified. 7 It will be appreciated that once the cryostat is in operation the helium supply 22 may be used only to afford make-up gas since the major portion of the helium entering the system is continuously recycled. Therefore conduit 23 contains a suitable valve 33 which is used to introduce any necessary make-up helium into the cycle. A suitable conduit 26 withdraws the low-pressure, essentially room temperature helium from the cryostat for use as the primary fluid source in the cycle. Compressors 28 and 29 are provided for pressurizing the helium which after passing through filter 30 and a suitable flow control means 25 is introduced into the cryostat cycle through conduit 31 which leads to the main heat exchanger. Valves 32 and 35 are provided to make it possible to use one or both of the compressors, an arrangement which gives greater flexibility and offers the opportunity of achieving the most economical operation. A gas holder 27' and engine pressure regulator valve 36 provide the necessary control of the high-pressure gas entering the system.

The components within the cryostat make up the primary portion of the apparatus of this invention. In

- FIG. 1 it will be seen that there is provided first a main heat exchanger 40 which has a high-pressure side 39 and a low-pressure side 41. It should be pointed out that in presenting FIG. 1 in a diagrammatic fashion it was necessary to draw the heat exchangers 40 and 60 in such a manner as to permit showing the other components of the equipment in the dewar-type housing in a way which could be easily comprehended and understood. In actual practice main heat exchanger 40 is, in a preferred embodiment, finned tubing passing through a narrow annular space in which the high-pressure gas flows within the tubing and the low-pressure gas flows in the passage surrounding it. Moreover, the finned tubing and its associated passage around it is located adjacent to the inside of inner wall 12 so that it might obtain the full advantage of heat exchange with the liquid nitrogen in the precooling coils. The charcoal traps and expansion engines decribed below are preferably located within a space defined by main heat exchngers 40 and 60. Modifications of such an arrangement are within the skill of anyone familiar with the art, and the important part of the invention lies in the manner in which the fluid is circulated.

If gases other than helium are to be used as refrigerants or to be liquefied, then it may be desirable to modify the apparatus in accordance with the teaching in US. Patent 2,909,903. This modification shows the use of a helical channel between the main heat exchanger 40 and precooling coils 18. FIG. 1 of US. Patent 2,909,903 clearly illustrates the relative arrangement and position of heat exchangers 40 and 60 with relation to the precooling coils 18 and radiation shield 16.

In order to remove contaminants from the fluid which is to be cooled or liquefied two charcoal traps 42 and 44 are provided through which the high-pressure gas is serially circulated. These remove contaminants which liquefy or solidify at the temperature which the fluid has reached at that point in the heat exchanger at which the fluid is removed for introduction into the traps. Suitable conduits 43 and 45 are provided for conducting the highpressure fluid through these charcoal traps. It will be appreciated that any other purifying means which can operate at the temperatures involved and which are capable of removing liquefied or solidified contaminants may also be used in place of the traps 42 and 44. At the coldest end 46 of main heat exchanger 40 all of the highpressure cold gas is removed from the high-pressure side 39 and by way of charcoal trap 44 it is introduced into a manifold line 48 which is divided into lines 49, 50 and 51, these lines leading directly into expansion engines 54 and 56 and Joule-Thomson valve 58, respectively. Thus it will be seen that the plurality of expansion engines, in-

cluding the Joule-Thomson valve, are in parallel relation-- ship. The advantage of this arrangement lies in the fact that the gas as it is extracted from the cold end of the main heat exchanger 40 is reduced to a very low temperature, thus increasing the density of the fluid and permitting both of the expansion engines 54 and 56 to handle a greater mass flow of fluid than if they were placed in series with respect to each other.

That portion of the cold fluid which is introduced into line 51 is taken through a secondary heat exchanger 60 (having a high-pressure side 59 and a low-pressure side 61) prior to introduction into the Joule-Thomson valve 58. In order to efliciently separate the helium liquefied in the Jule-Thomson valve from the cold gas, it has been found desirable to introduce the fluid from the Joule- Thomson valve into diffuser 62 which separates the liquid from the gas and directs the extremely cold gas up through the low-pressure side 61 of the secondary heat exchanger 60- into conduit 63 which is controlled by valve 64 and which leads to the cold, low-pressure side 41 of main heat exchanger 40. With valve 64 open the cold gas which is not liquefied in the J oule-Thomson valve is returned to the heat exchanger 40, A suitable vacuum-jacketed conduit 55 having valve 57 permits withdrawal of liquefied gas 21 which, has collected at the bottom. The presence of the liquid helium in the bottom of the dewar-type container and the cold helium gas in equilibrium above it rneans that the entire apparatus within the vessel is exposed to cold helium gas and hence a temperature gradient.

In a preferred embodiment, the expansion engines 54 and 56 are wrapped with glass wool or other suitable material to avoid refrigeration losses which would otherwise be caused by the free convection about the engines brought about as a result of the inversion of temperature going from the top to the bottom of the apparatus.

Turning now to that portion of the cycle which includes the expansion engines 54 and 56, it will be seen that the cold gas which is delivered by these expansion engines through conduit 66 may be, by opening valves 67 and 71, sent to an external load through a vacuum-jacketed conduit 68. The cold gas is taken out through vacuumjacketed line 68 and is returned through a vacuumjacketed conduit 72 through valve 71 and conduit 70 to the cold, low-pressure side 41 of the main heat exchanger 40. During refrigerating, valve 58 will be closed so that no liquefaction is achieved, and valve 64 will be closed so that the cold gas from expansion engines 54 and 56 cannot return directly through heat exchanger 40. It will normally be desirable to have means for measuring the temperature of the cold gas leaving the cryostat to the external load and of the gas returning to the cryostat from the external load. This is conveniently achieved by placingthermocouples 74 and 76 in contact with conduits 66 and 70 just beyond the point where the vacuum jacket begins on the conduits. Lead. wires 75 and 77 are connected to temperature measuring means 74 and 76, respectively, and are brought outside the cryostat for recordation and observation of temperatures. These temperature measuring means may be thermocouples, gas thermometers or any other suitable like devices.

FIG. 2 represents a modification of the cryostat of r FIG. 1 and it will be understood that the components shown in FIG. 2 are located within a dewar-type housing with the same type of precooling and the same type of auxiliary components as those illustrated in FIG. 1. Although both of the modifications'shown in FIGS. 1 and 2 are designed to furnish refrigeration or to liquefy gas, that of FIG. 1 has a higher refrigeration capacity than that of FIG. 2 for essentially the same equipment and mass flow rate. On the other hand, the modification of FIG. 2 has the higher liquefaction capacity for essentially the same equipment and mass flow rate.

The apparatus of FIG. 2 differs from that of FIG. 1 in that the former has valves 84 and 86 which can be used to control the balance of the flow of high-pressure fluid flowing from two different temperature levels of the highpressure side 39 of heat exchanger 40 to the expansion engines 54 and 56. This is accomplished first by drawing off the cold high-pressure fluid through conduit 80 from the high-pressure side 39 of main heat exchanger 40 somewhat above the very end 46 to complete removal of contaminants in charcoal trap 44.

All of the valves locate-d within the enclosed portion of the apparatus are preferably extended-stem valves, making them accessible from the outside. This in turn means that the apparatus may be switched back and forth between refrigerating and liquefying without taking any of it apart or even opening the enclosure or housing. It will be appreciated that this achieves true flexibility in the apparatus with respect to the type of performance desired. a

. The modfication illustrated in FIG. 1 is designed primarily to furnish cold gas for refrigerating an external load. In the operation of the apparatus of FIG. 1 if it is desired to use it as a refrigerator then valves 58 and 64 are closed. It will be seen that under these circumstances the gas coming from the cold high pressure end of main heat exchanger 40 by way of charcoal trap 44 is all distributed to expansion engines 54 and 56 and none of it is permitted to pass through the Joule-Thomson valve 58. The cold, high-pressure gas passing through expansion engines 54 and 56 is expanded and cooled, and by way of conduit 66 and valve 67 it is introduced into vacuum jacketed conduit 68 which takes the cold refrigenating gas to the external load. The gas returning from the external load comes by way of vacuumjacketed line 72 and through valve 71, and by way of conduit 70 it is returned through the low-pressure side 41 of heat exchanger 40 at point 65. In both FIGS. 1 and 2 the solid arrows indicate the flow of fluid when the apparatus is used in liquefying a gas while dotted arrows illustrate the flow of the fluid in that portion of the apparatus which is directed toward furnishing refrigeration to an external load.

One of the major advantages of the apparatus and method of this invention lies in the fact that the refrigeration cycle is closed. By returning the refrigerating gas from the external load to the system to be put through the heat exchanger, essentially no make-up gas is required. Thus, the gas supply is conserved and the refrigeration in the gas is used to its fullest advantage.

If it is decided to use the apparatus of FIG. 1 to liquefy a gas then valves 67 and 71 are closed and valves 58 and 64 are opened. Now the gas which passes through expansion engines 54 and 56 is returned by means of valve 64 into the low-pressure side 41 of heat exchanger 40 while that gas which enters conduit 51 passes through the secondary heat exchanger 60 into the Joule-Thomson valve 58 where a portion of it is liquefied through additional expansion. The fluid from Joule-Thomson valve 58 is then introduced into diffuser 62 which separates the gas from the liquid. The liquid is permitted to accumulate as liquid 21 in the bottom of the dewar while the cold gas now at low pressure passes up through the lowpressure side 61 of heat exchanger 60 and by way of conduit 63 (controlled by valve 64) it enters the low-pressure side 41 of the main heat exchanger 40.

The modification in FIG. 2 is designed to be used equally well as a refrigerator or as a source of liquefied gas. When the apparatus of FIG. 2 is to be used for liquefying gas, valves 67, 71 and 86 are closed, while valves 64, 84 and 58 are open. In this arrangement all of the gas which enters expansion engines 54 and 56 goes through valve 84 and the resulting expanded cooled gas is returned to the low pressure side of the main heat exchanger through valve 64 at the point indicated :at 65. That portion of the gas which is to be introduced into the Joule-Thomson valve 58 after passing through charcoal trap 44 is returned to the main heat exchanger 40 by means of conduit 82 at a point 83 which is somewhat above the low-temperature end of that heat exchanger. It is then put through the high-pressure side of secondary heat exchanger 6% to enter Joule-Thomson valve 58. It is thus possible to cool the gas which is entering heat exchanger 66 and Joule-Thomson valve 58 much more efficiently.

It will be appreciated that there is a far greater mas; flow of cold low-pressure gas in the lower part of heatexchanger 40 than there is of high-pressure gas to be cooled. Thus in that lower portion of heat exchanger 40 corresponding to the section between the point where conduit 82 joins the high-pressure side 39 at 83 and where the highpressure gas leaves the heat exchanger 40 at 46, only that part of the high-pressure gas going to the Joule-Thomson valve 58 is circulated while all of the gas in the cycle which is not liquefied is circulated through. the low-pressure side 41 to cool the gas destined for the Joule-Thomson valve. As a result the gas on the way to the Joule-Thomson valve gets much more efiicient cooling for it exchanges heat with all of the exhaust gas flow of expansion engines 54 and 56 as well as with nonliquefied portion of the cold gas that has gone through heat exchanger 60, Joule-Thomson valve 58 and diffuser 62. Thus by establishing an imbalance in the mass flow of the gas an improved cooling of that portion of the gas which is to be liquefied is achieved. In this manner it will be seen that the apparatus of FIG. 2 is particularly well adapted to furnishing relatively large quantities of a liquefied gas.

The apparatus in FIG. 2 however equally adapted to furnishing refrigeration to an external load. If this is to be accomplished and no liquefaction is desired then valve 64 and Joule-Thomson valve 58 will be closed while valves 84, 86, 67 and 71 will be open. Actually valves 84 and 86 may be throttled to obtain specific types of conditions to get optimum refrigeration with a given temperature.

Under these circumstances it will be seen that cold, high-pressure gas may enter the expansion engines 54 and 56 through the conduit lines controlled by both valves 84 and 86 while none of the cold high-pressure gas is permitted to flow through the Joule-Thomson valve 58. With valve 64 closed the cold expanded gas from expansion engines 54 and 56 passes by way of conduits 66 and valve 67 into vacuum-jacketed line 68 to an external load. The refrigerating gas is then returned from the external load by way of vacuum-jacketed line 72, valve 71 and conduit 70 as in the case of the apparatus of FIG. 1.

It will be seen from the above description of the apparatus and the method in which it may operate that there is provided by this invention a means and method for furnishing either a liquefied gas or for furnishing cold;

gas for refrigerating an external load. Thus the apparatus is completely flexible and can provide a source of liquefied gas or refrigerating gas.

We claim:

l. A closed-cycle cryogenic apparatus adapted to be employed in the dual capacity of refrigerator and liquefier into which a high-pressure cryogenic fluid is introduced, cooled, expanded and then withdrawn as lowpressure fluid, comprising in combination (a) a first heat exchanger adapted to exchange heat between fluid streams in a high-pressure passage and a low-pressure passage;

'(b) a second heat exchanger adapted to exchange heat between fluid streams in a highapressure passage and a low-pressure pas-sage;

(c) a first main fluid path communicating between the high-pressure passages of said first and second heat exchangers; I

(d) a'second main fluid path communicating between the low-pressure passages of said first and second heat exchangers;

(e) fluid conduit means adapted to circulate cold expanded fluid to a load external of said apparatus and having inlet and outlet terminals within said apparatus;

(f) a first auxiliary fluid path communicating between the high-pressure passage of said first heat exchanger and the inlet terminal of said fluid conduit means;

(g) a second auxiliary fluid path communicating between the outlet terminal of said fluid conduit means and said second main fluid path;

(h) a first fluid expansion means located in said first auxiliary fluid path;

(i) a, third auxiliary fluid path connecting the highpressure and low-pressure passages of said second heat exchanger;

(j) a second fluid expansion means and associated diffuser means located in said third auxiliary fluid path, said means being adapted to liquefy at least a portion of the high p-ressure fluid entering said second fluid expansion means and to return cold low-pressure fluid to said low-pressure passage of said second heat exchanger; and

, (k) fluid flow control means located between said first auxiliary fluid path and said low-pressure path of said first heat exchanger and in said first, second and third auxiliary fluid paths, whereby the operation of said fluid flow control means permits a choice between (1) directing high-pressure fluid into said second expansion means with resulting production of liquefied fluid and concurrent return of cold lowpressure fluid from said first expansion means to .said low-pressure passage of said first heat exchanger, and (2) directing cold low-pressure fluid from said first expansion means through said fluid conduit means with resulting delivery of refrigeration to said load and return of said fluid to said second main path.

2. A cryogenic apparatus in accordance with claim 1 wherein said first fluid expansion means comprises a pair of expansion engines arranged in parallel and adapted to deliver work external of said system.

3. A cryogenic apparatus in accordance with claim 1 wherein said second fluid expansion means comprises a Joule-Thomson valve which serves also as said fluid flow control means in said third auxiliary fluid path.

4. A cryogenic apparatus in accordance with claim 1 further characterized by having gas purifying means associated with said high-pressure passage of said first heat exchanger arranged to remove impurities condensed out of said high-pressure fluid during its passage through said first heat exchanger.

5. A cryogenic apparatus in accordance with claim 1 wherein said first auxiliary fluid path comprises valvecontrolled branched conduits terminating in a common conduit, said branched conduits being connected to said high-pressure passage of said first heat exchanger at different temperature levels.

6. A cryogenic apparatus in accordance with claim 1 further characterized by having precooling coils surrounding said first and second heat exchangers and being adapted to circulate a liquefied gas therethrough.

7. A closed-cycle cryogenic apparatus adapted to be employed in the dual capacity of refrigerator and liquefier into which a high-pressure cryogenic fluid is intro duced, cooled, expanded, and then withdrawn as low pressure fluid, comprising in combination (a) first and second in-series heat exchangers, each being adapted to convey high-pressure fluid within a high-pressure passageway and low-pressure fluid within a lowapressure passageway, said passageways being in out-of-contact heat exchange relationship;

(b) first and second expansion means, said second expansion means being adapted to liquefy at least a portion of said high-pressure fluid delivered thereto;

(c) conduit means arranged to convey said high-pressure fluid into the high-pressure passageway of said first heat exchanger;

(d) conduit means arranged to convey a first portion of initially cooled high-pressure fluid from said highpressure passageway of said first heat exchanger near its colder end to said first expansion means and a second portion of said initially cooled high-pressure fluid into said high-pressure passageway of said second heat exchanger and thence to said second expansion means;

(e) means for controlling the amount of flow of said high-pressure fluid to at least said second expansion means, thereby to control the .amount of said fluid to be liquefied;

(f) conduit means for conveying cold, low-pressure fluid from said first expansion means to said lowpressure passageway of said first heat exchanger and to and from an external load, including means for controlling the flow of low pressure fluid to said external load and to said low-pressure passageway of said first heat exchanger, whereby operation of said means for controlling the amount of flow of high-pressure fluid to said second expansion means and said means for controlling the flow of low-pressure fluid to said external load permits a choice between the liquefaction of said fluid the delivery of refrigenationto an external load; and

(g) controlled-flow conduit means for conveying lowpressure gas from said second heat exchanger to said low-pressure passageway of said first heat exchanger.

8. A cryogenic apparatus in accordance with claim 7 75 where-in said first expansion means comprises a pair of expansion engines arranged in parallel and are adapted to deliver work external of said system, and said second expansion means is a Joule-Thomson valve.

9. A cryogenic apparatus in accordance with claim 7 further characterized by having gas purifying means associated with said high-pressure passageway of said first heat exchanger arranged to remove impurities condensed out of said compressed gas during its passage through said first heat exchanger.

10. A cryogenic apparatus in accordance with claim 7 further characterized by having precoolin-g coils surrounding said first and second heat exchangers and being adapted to circulate a liquefied gas therethrough.

11. A low-temperature fluid refrigeration system, comprising in combination (a) a source of compressed gas;

('b) first and second heat exchangers, each being adapted to handle high-pressure gas within a highpressure passageway and low-pressure gas within a low-pressure passageway, said passageways being in out-of-contact heat exchange relationship;

(c) conduit means arranged to convey said compressed gas into said high-pressure passageway of said first heat exchanger;

(d) first and second gas purifying means associated with said high-pressure passageway of said first heat exchanger and adapted to remove impurities condensed from said compressed gas during its passage through said high-pressure passageway of said first heat exchanger;

(e) first expansion means comprising expansion engines arranged in parallel and'adapted to expand compressed gas with the performance of external work;

(f) second expansion means comprising a Joule-Thomson valve adapted to expand cool compressed gas thereby to liquefy at least a portion thereof;

(g) conduit means adapted to convey cooled compressed gas from the cold end of said high-pressure passageway of said first heat exchanger to said second gas purifying means;

(h) first branch conduit means leading from said.

second purifying means to said expansion engines;

(i) conduit means adapted to transfer cold low-pressure gas from said engines to said low-pressure passageway of said first heat exchanger;

(j) second branch conduitmeans connecting said secr ond purifying means to said high-pressure passageway of said second heat exchanger and thence to said Joule-Thomson valve;

(k) means forcontrolling the amount of flow of compressed gas to said Joule-Thomson valve;

(1) thermally insulated conduit means for carrying cold low-pressure gas from said expansion engines to and from an external load including means for controlling the flow of said gas to said external load and means forreturning said low-pressure gas from said external load to said low-pressure passageway of "said first heat exchanger;

(m) diffuser means adapted to receive expanded gas from said Joule-Thomson valve thereby to separate liquid from gas and communicating with said lowpressure passageway of said second heat exchanger;

(n) controlled-flow conduit means for conveying lowpressure gas from said low-pressure passageway of said second heat exchanger to said low-pressure passageway of said first heat exchanger;

() precooli-ng coils surrounding said first and second heat exchangers and being adapted to circulate a liquefied gas therethrough; and

(p) dewar-type vessel means enclosing and thermally insulating said system exclusive of said source of compressed gas.

12. A low-temperature fluid refrigeration system, comprising in combination (a) a source of compressed gas;

(1)) first and second heat exchangers, each adapted to handle high-pressure gas within a high-pressure passageway and low-pressure gas within a low-pressure passageway, said passageways being in out-of-contact heat exchange relationship;

(0) conduit means arranged to convey said compressed gas into said high-pressure passageway of said first heat exchanger;

(d) first and second gas purifying means associated with said high-pressure passageway of said first heat exchanger and adapted to remove impurities condensed from said compressed gas during its passage through said high-pressure passageway of said first heat exchanger;

(e) first expansion means comprising expansion engines arranged in parallel and adapted to expand compressed gas with the performance of external 1 work;

(f) second expansion means comprising a Joule-Thomson valve adapted to expand cool compressed gas thereby to liquefy at least a portion thereof;

(g) conduit means arranged to convey cooled compressed gas from the high-pressure passageway of said first heat exchanger at a point adjacent, but spaced from, the cold end thereof to said second gas purifying means;

(h) first branch conduit means leading from said second purifying means to said expansion engines;

(i) second branch conduit means communicating between said second purifying means and said cold end 'of said highapressul'e passageway of said first heat exchanger at a point downstream from said firstmentioned point;

(j) third branch conduit means communicating with said cold end of said highapressure passageway of said first heat exchanger and adapted to convey cooled compressed gas into said high-pressure passageway of'said second heat exchanger and thence to said Joule-Thomson valve;

,(k) a high-pressure by-pass conduit communicating between said cold end of said high-pressure passageway 'of said first heat exchanger and the inlets of said expansion engines;

(1) means for controlling the amount of flow of compressed gas passing through said first branch conduit, said third branch conduit and said highpressure by-pass conduit;

(in) conduit means adapted to transfer cold low-pressure gas from said engines to said low-pressure passageway of said second heat exchanger;

(11) thermally insulated conduit means for carrying cold low-pressure gas from said expansion engines to and from an external load including means for controlling the flow of said gas to said external load and means for returning said low-pressure gas from said external load to said low-pressure passageway of said first heat exchanger;

(0) diffuser means adapted to receive expanded gas from said Joule-Thomson valve thereby to separate liquid from gas and communicating with said lowpressure passageway of said second heat exchanger;

(p) controlled flow conduit means for conveying lowpressure gas from said low-pressure passageway of said second heat exchanger to said low-pressure passageway of said first heat exchanger;

(q) .precooling coils surrounding said first and second heat exchangers and being adapted to circulate a liquefied gas therethrough; and

(r) dewar-type vessel means enclosing and thermally insulating said system exclusive of said source of compressed gas.

(References on following page) 1 1 1 2 References Cited by the Examiner I 2,932,173 4/ 1960 Mordh'orst 62--9 2,937,076 5/1960 Class.

UNITED STATES PATENTS 2,957,318 10/ 1960 Morrison 62-87 X 1 /1949 Collins 62 4() X 3,066,492 12/ 1962 Grunberg 629 1 1950' Fen-o 62 7 5 3,098,732 6/1963 Dennis 6240 X 8/ 1956 Sixsmith 629 7/1959 Sweeter NORMAN YUDKOFF, Przmary Examzner.

10/1959 J. JOHNSON, Assistant Examiner.

Zimmermann 62-40 X 

1. A CLOSED-CYCLE CRYOGENIC APPARATUS ADAPTED TO BE EMPLOYED IN THE DUAL CAPACITY OF REFRIGERATOR AND LIQUEFIER INTO WHICH A HIGH-PRESSURE CRYOGENIC FLUID IS INTRODUCED, COOLED, EXPANDED AND THEN WITHDRAWN AS LOWPRESSURE FLUID, COMPRISING IN COMBINATION (A) A FIRST HEAT EXCHANGER ADAPTED TO EXCHANGE HEAT BETWEEN FLUID STREAMS IN A HIGH-PRESSURE PASSAGE AND A LOW-PRESSURE PASSAGE; (B) A SECOND HEAT EXCHANGER ADAPTED TO EXCHANGE HEAT BETWEEN FLUID STREAMS IN A HIGH-PRESSURE PASSAGE AND A LOW-PRESSURE PASSAGE; (C) A FIRST MAIN FLUID PATH COMMUNICATING BETWEEN THE HIGH-PRESSURE PASSAGES OF SAID FIRST AND SECOND HEAT EXCHANGERS; (D) A SECOND MAIN FLUID PATH COMMUNICATING BETWEEN THE LOW-PRESSURE PASSAGES OF SAID FIRST AND SECOND HEAT EXCHANGERS; (E) FLUID CONDUIT MEANS ADAPTED TO CIRCULATE COLD EXPANDED FLUID TO A LOAD EXTERNAL OF SAID APPARATUS AND HAVING INLET AND OUTLET TERMINALS WITHIN SAID APPARATUS; (F) A FIRST AUXILIARY FLUID PATH COMMUNICATING BETWEEN THE HIGH-PRESSURE PASSAGE OF SAID FIRST HEAT EXCHANGER AND THE INLET TERMINAL OF SAID FLUID CONDUIT MEANS; (G) A SECOND AUXILIARY FLUID PATH COMMUNICATING BETWEEN THE OUTLET TERMINAL OF SAID FLUID CONDUIT MEANS AND SAID SECOND MAIN FLUID PATH; (H) A FIRST FLUID EXPANSION MEANS LOCATED IN SAID FIRST AUXILIARY FLUID PATH; (I) A THIRD AUXILIARY FLUID PATH CONNECTING THE HIGHPRESSURE AND LOW-PRESSURE PASSAGES OF SAID SECOND HEATER EXCHANGER; 